An unusual crystal growth method of the chalcohalide semiconductor, β-Hg 3 S 2 Cl 2 : A new candidate for hard radiation detection
Here, we assess the mercury chalcohalide compound, β-Hg 3 S 2 Cl 2 , as a potential semiconductor material for X-ray and γ-ray detection. It has a high density (6.80 g/cm 3 ) and wide band gap (2.56 eV) and crystallizes in the cubic Pm4$\bar{3}$n space group with a three-dimensional structure comprised of [Hg 12 S 8 ] cubes with Cl atoms located within and between the cubes, featuring a trigonal pyramidal SHg3 as the main building block. First-principle electronic structure calculations at the density functional theory level predict that the compound has closely lying indirect and direct band gaps. We have successfully grown transparent, single crystals of β-Hg 3 S 2 Cl 2 up to 7 mm diameter and 1 cm long using a new approach by the partial decomposition of the quaternary Hg 3 Bi 2 S 2 Cl 8 compound followed by the formation of β-Hg 3 S 2 Cl 2 and an impermeable top layer, all happening in situ during vertical Bridgman growth. The decomposition process was optimized by varying peak temperatures and temperature gradients using a 2 mm/h translation rate of the Bridgman technique. Formation of the quaternary Hg 3 Bi 2 S 2 Cl 8 followed by its partial decomposition into β-Hg 3 S 2 Cl 2 was confirmed by in situ temperature-dependent synchrotron powder diffraction studies. The single crystal samples obtained had resistivity of 10 10 Ω·cm and mobility-lifetime products of electron and hole carriers of 1.4(4) × 10 –4 cm 2 /V and 7.5(3) × 10 –5 cm 2 /V, respectively. Further, an appreciable Ag X-ray photoconductivity response was observed showing the potential of β-Hg 3 S 2 Cl 2 as a hard radiation detector material.